1. Field of the Invention
The present invention relates to heat dissipation techniques, and more particularly, to a loop type heat dissipating apparatus for use with an active cooling technique.
2. Description of the Prior Art
As the electronic and information industries continue to develop, people nowadays have visions of owning electronic products which are multi-function, fast at computation and miniaturized. Manufacturers make efforts to enhance the performance of electronic products, thus producing electronic products which are more and more power-consuming. What the manufacturers are also multiplying is the heat flux of a heat source inside the electronic products produced, such as a CPU, laser diode, LED array, and multi-chip module (MCM). Hence, great importance is attached to rapid heat transfer across tiny space inside an electronic product.
Taking a CPU as an example, existing designs of heat dissipations are, namely a heat spreader, a heat pipe disposed between cooling fins, a loop heat pipe, a droplet-cooling heat dissipating apparatus, and etc.
There are patents related to a heat dissipating apparatus with a heat spreader, namely Taiwanese utility model Nos. M270407 and M260724. The purpose of a heat spreader is to take in heat evenly and thereby prevent uneven heat dissipation. Nevertheless, the performance of a conventional cooler equipped with a heat spreader is subject to the thermal conductivity of a constituent material and thereby achieves only passive cooling, thus being unfit to meet the increasingly strict requirements for heat dissipation.
There are patents related to a heat pipe, namely Taiwanese Patent Nos. I241156, I236337, I225584, and etc. A heat pipe removes a huge amount of heat by phase change. Referring to FIG. 1, a conventional heat pipe 10 is filled with a working fluid, and the direction in which the liquid phase of the working fluid flows 101 is opposite to the direction in which the gaseous phase of the working fluid flows 103.
However, in so doing, thermal resistance increases and thereby limits the maximum quantity of heat transferred. In addition, the heat pipe 10 using a wick structure 109 is disadvantaged due to great flow resistance and thereby unfit to deal with great heat flux. Last but not least, a conventional heat pipe has drawbacks, such as short heat transfer distance and small contact surface area.
There are patents related to a loop type heat dissipating apparatus, namely Taiwanese Patent Nos. 508487 and 502101. A conventional loop type heat dissipating apparatus, such as a micro loop heat pipe, is shown in FIG. 2 which depicts a loop type heat dissipating apparatus 20 comprising an evaporator 201 and a condenser 203 working in conjunction with a liquid phase working fluid channel 205 and a gaseous phase working fluid channel 207 spaced apart therefrom, thus the loop type heat dissipating apparatus 20 is spatially flexible and capable of long-distance heat transfer.
Although the liquid phase of the working fluid returns to the condenser 203 after being evaporated by the evaporator 201, the liquid phase of the working fluid forms a liquid film (not shown) at the bottom of the evaporator 201 and thereby increases the thermal resistance of the heat dissipating apparatus.
Taiwanese Patent No. I251656 discloses a pool boiling heat dissipating apparatus which comprises a buffer space whereby a boiling fluid steadily comes into contact with a heat dissipating surface. However, as stated in J. Yang, “Spray Cooling with an Air Atomizing Nozzle,” Ph. D. Thesis, University of Kentucky, Lexington, Ky., 1993, taking water as an example, the heat transfer coefficient of a pool boiling heat dissipating apparatus is 5×104 W/m2K approximately, whereas that of spray cooling exceeds 5×105 W/m2K, and thus the performance of a heat dissipating system can be enhanced by spray cooling.
A droplet cooling device disclosed in Embedded Droplet Impingement for Integrated Cooling of Electronics (EDIFICE) presented by the America-based Carnegie Mellon University involves spraying microdroplets to an area where a hot spot is created on a heat source, removing heat from the hot spot by phase change of the microdroplets, conveying vapor to a condenser having a heat sink, such as a cooling fin, a cooler, and a fan, by a vapor conveying path, condensing the vapor to liquid, and sending the liquid to micro-orifices under a pressure gradient provided by a driving pump, so as to keep the heat dissipation cycle going and provide the cooling function.
Nonetheless, a droplet cooling device based on spray cooling requires an external pump to expel droplets out of micro-orifices, which increases the overall volume inevitably and therefore fails to meet the requirements for product miniaturization.
Accordingly, an issue that needs an urgent solution is related to endeavors to overcome the aforesaid drawbacks of the prior art.